1. Field of the Invention
The present invention relates to a spin-valve type thin film element in which electrical resistance changes in response to the relationship between the magnetization direction of a pinned magnetic layer and the magnetization direction of a free magnetic layer which is influenced by an external magnetic field. More particularly, the invention relates to a spin-valve type thin film element in which a relative angle between the magnetization of a pinned magnetic layer and the magnetization of a free magnetic layer can be properly adjusted.
2. Description of the Related Art
FIG. 7 is a sectional view of a spin-valve type thin film element (spin-valve type thin film magnetic head) which detects a recording magnetic field from a recording medium such as a hard disk drive.
This spin-valve type thin film element includes an antiferromagnetic layer 10, a pinned magnetic layer 11, a non-magnetic electrically conductive layer 12, and a free magnetic layer 13 deposited in that order, and hard magnetic bias layers 5 and 5 formed on both sides thereof.
Generally, a nickel-manganese (Nixe2x80x94Mn) alloy film is used for the antiferromagnetic layer 10, a nickel-iron (Nixe2x80x94Fe) alloy film is used for the pinned magnetic layer 11 and the free magnetic layer 13, a copper (Cu) film is used for the non-magnetic electrically conductive layer 12, and a cobalt-platinum (Coxe2x80x94Pt) alloy film or the like is used for the hard magnetic bias layers 5 and 5. Numerals 6 and 7 represent an under layer and a protective layer, respectively, composed of a non-magnetic material such as tantalum (Ta).
As shown in the drawing, the antiferromagnetic layer 10 and the pinned magnetic layer 11 are formed in contact with each other, the pinned magnetic layer 11 is put into a single domain state in the Y direction by an exchange anisotropic magnetic field caused by exchange coupling at the interface between the pinned magnetic layer 11 and the antiferromagnetic layer 10, and the magnetization direction is fixed in the Y direction. The exchange anisotropic magnetic field occurs at the interface between the antiferromagnetic layer 10 and the pinned magnetic layer 11 by film deposition or annealing while applying the magnetic field in the Y direction.
Also, the magnetization direction of the free magnetic layer 13 is aligned in the X direction under the influence of the hard magnetic bias layers 5 and 5 which are magnetized in the X direction.
In the spin-valve type thin film element, a sensing current is applied from electrically conductive layers 8 and 8 formed on the hard magnetic bias layers 5 and 5 into the pinned magnetic layer 11, the non-magnetic electrically conductive layer 12, and the free magnetic layer 13. The driving direction of a recording medium such as a hard disk drive is in the Z direction, and if a leakage magnetic field from the recording medium is applied in the Y direction, the magnetization of the free magnetic layer 13 changes from the X direction to the Y direction. Because of the relationship between the change in the magnetization direction in the free magnetic layer 13 and the pinned magnetization direction of the pinned magnetic layer 11, the electrical resistance changes, and the leakage magnetic field from the recording medium is detected by the voltage change based on the change in the electrical resistance.
Although the hard magnetic bias layers 5 and 5 are formed to put the free magnetic layer 13 into a single domain state and align the magnetization in the X direction shown in the drawing, the magnetization of the free magnetic, layer 13 is not always aligned in the X direction in the entire region when a sensing current is applied.
Japanese Patent Publication No. 9-92907 (page 2, column 2, line 14) describes that xe2x80x9cin the magnetoresistive element, the first ferromagnetic layer 21 is subjected to a magnetic field caused by static magnetic coupling with the second ferromagnetic layer 23, a magnetic field caused by exchange coupling between layers, and an electric current magnetic field.xe2x80x9d The xe2x80x9cfirst ferromagnetic layer 21xe2x80x9d corresponds to the free magnetic layer 13 shown in FIG. 7, and the xe2x80x9csecond ferromagnetic layer 23xe2x80x9d corresponds to the pinned magnetic layer 11 shown in FIG. 7.
The above Patent Publication also has the following description (page 2, column 2, line 23). xe2x80x9cHowever, each magnetic field essentially has a different distribution of height directions, and thus, complete offset cannot be performed. For example, FIG. 3A is a graphic representation showing the distribution of height directions with respect to the static magnetic field caused by static magnetic coupling, the electric current magnetic field and the magnetization in the first ferromagnetic layer. As is clear from the drawing, since the static magnetic field caused by static magnetic coupling and the electric current magnetic field are properties oriented in the same direction in relation to the vertical axis, the two magnetic fields cannot be offset uniformly, the height component of the magnetization of the first ferromagnetic layer crosses zero at both ends in the height direction. Thereby, magnetic domain walls are produced, which may lead to Barkhausen noise.xe2x80x9d
That is, as shown in FIG. 9, even when the static magnetic field caused by static magnetic coupling and the electric current magnetic field caused by a sensing current are offset with respect to the magnetization C2 in the central region in the Y direction (height direction) in the free magnetic layer 13, magnetizations C1 and C3 in end regions in the Y direction are inclined in relation to the X direction.
As described above, the free magnetic layer 13 has a distribution of different magnetization directions in relation to the Y direction under the influence of the static magnetic field caused by static magnetic coupling and the electric current magnetic field caused by a sensing current.
Therefore, as shown in FIG. 9, the relative angle between magnetizations C1 and C3 of the free magnetic layer 13 and the magnetization D of the pinned magnetic layer 11 is not set at 90xc2x0, and thus, asymmetry deteriorates. The word xe2x80x9casymmetryxe2x80x9d means the vertical asymmetry of the regenerated output waveform.
In Japanese Patent Publication No. 9-92907, an attempt is made to set at 90xc2x0 the relative angle between the magnetization of the first ferromagnetic layer (free magnetic layer) and the magnetization of the second ferromagnetic layer (pinned magnetic layer), as described in the following (page 3, column 3, line 17). xe2x80x9cFIG. 3B shows the distribution of height directions with respect to the static magnetic field caused by static magnetic coupling, the electric current magnetic field and the magnetization in the first ferromagnetic layer 1. In this distribution, the static magnetic field caused by static magnetic coupling and the electric current magnetic field are properties standing opposed to each other in relation to the vertical axis. Also, since the magnetization of the first ferromagnetic layer 1 is directed at 45xc2x0 in relation to the direction of the applied magnetic field, the magnetic fields are added, and thus, the first ferromagnetic layer 1 has substantially uniform height components of the magnetization in relation to the height direction.xe2x80x9d
That is, as shown in FIG. 10, the magnetization D of the second ferromagnetic layer (pinned magnetic layer 11) is fixed, being inclined by xcex82 (=45xc2x0) in relation to the Y direction, and because of static magnetic coupling with the pinned magnetic layer 11, the magnetization C2 of the first ferromagnetic layer (free magnetic layer 13) is inclined by xcex82 (=45xc2x0). The relative angle between magnetizations C1, C2, and C3 of the free magnetic layer and the magnetization D of the pinned magnetic layer is adjusted to 90xc2x0, and thus, the static magnetic field and the electric current magnetic field are offset.
Japanese Patent Publication No. 9-92907 aims to overcome the problem of asymmetry by the method described above.
However, it has been confirmed that the magnetization of the free magnetic layer 13 in the central region has a different direction from that in end regions in relation to the track width direction (X direction). The magnetization state is shown in FIG. 8.
As shown in FIG. 8, magnetizations A and B in end regions of the free magnetic layer 13 are easily aligned in the X direction. The reason is that the end regions of the free magnetic layer abut on hard magnetic bias layers 5 and 5, and are strongly influenced by the bias magnetic field of the hard magnetic bias layers 5 and 5 in the X direction.
In accordance with Japanese Patent Publication No. 9-92907, although the relative angle between magnetizations C1, C2, and C3 in the central region of the free magnetic layer 13 and the magnetization D2 of the pinned magnetic layer 11 can be set at 90xc2x0 or its approximation, since magnetizations D1, D2, and D3 of the pinned magnetic layer 11 are fixed so as to be inclined in relation to the Y direction, the relative angle between magnetizations A and B in end regions of the free magnetic layer 13 and magnetizations D1 and D3 of the pinned magnetic layer 11 cannot be set at 90xc2x0, resulting in the deterioration of asymmetry in the end regions.
The deterioration of asymmetry in the end regions makes it difficult to detect the track position accurately, and easily leads to a servo error.
The present invention overcomes the problems noted above with respect to the related art. It is an object of the present invention to provide a spin-valve type thin film element in which, in the presence of an applied sensing current, magnetizations in end regions and the central region of a pinned magnetic layer are properly aligned so that the relative angle between the magnetization of a free magnetic layer and the magnetization of the pinned magnetic layer in the entire region is set at 90xc2x0, and thus, satisfactory asymmetry can be obtained.
In accordance with the present invention, a spin-valve type thin film element includes an antiferromagnetic layer; a pinned magnetic layer formed in contact with the antiferromagnetic layer, the magnetization direction of the pinned magnetic layer being fixed by the exchange anisotropic magnetic field between the pinned magnetic layer and the antiferromagnetic layer; a free magnetic layer formed over and/or under the pinned magnetic layer with a non-magnetic electrically conductive layer therebetween; a bias layer for aligning the magnetization direction of the free magnetic layer in the direction perpendicular to the magnetization direction of the pinned magnetic layer; and an electrically conductive layer for applying a sensing current into the pinned magnetic layer, the non-magnetic electrically conductive layer, and the free magnetic layer. The magnetization direction of the pinned magnetic layer in the end regions in relation to the track width is fixed in the direction of the leakage magnetic field from a recording medium, and the magnetization of the pinned magnetic layer in the central region is fixed in the direction of the leakage magnetic field from a recording medium, and the magnetization of the pinned magnetic layer in the central region is fixed in the direction inclined in relation to the direction of the leakage magnetic field from the recording medium.
In accordance with the present invention, the magnetization direction of the pinned magnetic layer in the central region is set perpendicular to the magnetization of the free magnetic layer in the central region when a sensing current is applied.
Also, in accordance with the present invention, preferably the antiferromagnetic layer is composed of an antiferromagnetic material having a composition of XaMn100xe2x88x92a, where X is at least one element selected from the group consisting of Pd, Pt, Ru, and Ir, and the atomic percent xe2x80x9caxe2x80x9d satisfies 40xe2x89xa6axe2x89xa660.
In particular, in accordance with the present invention, among the Xxe2x80x94Mn alloys, a Ptxe2x80x94Mn alloy is more preferably used for the antiferromagnetic layer.
The Ptxe2x80x94Mn alloy produces a larger exchange anisotropic magnetic field in comparison with the Nixe2x80x94Mn alloy or the like that has been conventionally used for the antiferromagnetic layer, and has a high blocking temperature, and also has high corrosion resistance. These are excellent characteristics as the antiferromagnetic material.
Also, in accordance with the present invention, the antiferromagnetic layer may be composed of a Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy, where Xxe2x80x2 is at least one element selected from the group consisting of Ni, Pd, Rh, Ru, Ir, Cr, and Co.
Also, in accordance with the present invention, a method for making a spin-valve type thin film element includes the following steps, the spin-valve type thin film element having an antiferromagnetic layer, a pinned magnetic layer formed in contact with the antiferromagnetic layer, the magnetization direction of the pinned magnetic layer being fixed by the exchange anisotropic magnetic field between the pinned magnetic layer and the antiferromagnetic layer, a free magnetic layer formed on the pinned magnetic layer with a non-magnetic electrically conductive layer therebetween, a bias layer for aligning the magnetization direction of the free magnetic layer in the direction perpendicular to the magnetization direction of the pinned magnetic layer, and an electrically conductive layer for applying a sensing current into the pinned magnetic layer, the non-magnetic electrically conductive layer, and the free magnetic layer:
a step of forming a multi-layered film by depositing the antiferromagnetic layer, the pinned magnetic layer, the non-magnetic electrically conductive layer, and the free magnetic layer, in that order;
a step of magnetic annealing at a temperature T1 so that the magnetization of the pinned magnetic layer is adjusted to the direction inclined in relation to the direction of the leakage magnetic field from a recording medium;
a step of patterning the multi-layered film into a predetermined shape, and forming a bias layer on both sides of the multi-layered film, the bias layer having a coercive force that enables a permanent magnet;
a step of magnetizing the bias layer in the same direction as that of the leakage magnetic field from the recording medium at a lower temperature than the temperature T1;
a step of annealing without applying a magnetic field at a temperature T2 so that the magnetization of the pinned magnetic layer in the end regions in relation to the track width is adjusted to the same direction as that of the leakage magnetic field from the recording medium; and
a step of magnetizing the bias layer in the direction perpendicular to the direction of the leakage magnetic field from the recording medium at a lower temperature than the temperature T2.
In accordance with the present invention, the multi-layered film may be formed by depositing the free magnetic layer, the non-magnetic electrically conductive layer, the pinned magnetic -layer, and the antiferromagnetic layer, in that order. Alternatively, the multi-layered film may be formed by depositing the antiferromagnetic layer, the pinned magnetic layer, the non-magnetic electrically conductive layer, the free magnetic layer, the non-magnetic electrically conductive layer, the pinned magnetic layer and the antiferromagnetic layer, in that order from the bottom.
Also, the antiferromagnetic layer is preferably composed of an Xxe2x80x94Mn alloy (where X is at least one element selected from the group consisting of Pd, Pt, Ru, and Ir), and more preferably composed of a Ptxe2x80x94Mn alloy. As described above, preferably, the composition of X ranges from 40 to 60 atomic percent, and the balance corresponds to the composition of Mn.
Also, the antiferromagnetic layer may be composed of a Ptxe2x80x94Mnxe2x80x94Xxe2x80x2 alloy (where Xxe2x80x2 is at least one element selected from the group consisting of Ni, Pd, Rh, Ru, Ir, Cr, and Co).
Also, in accordance with the present invention, the temperature T1 preferably ranges from 200xc2x0 C. to 260xc2x0 C., the temperature T2 preferably ranges from 210xc2x0 C. to 270xc2x0 C., and, in particular, the temperature T2 is preferably set higher than the temperature T1.
In accordance with the present invention, the magnetization direction of the pinned magnetic layer is properly adjusted in response to the magnetization direction of the free magnetic direction.
Generally, the magnetization of the free magnetic layer is aligned in the track width direction under the influence of the bias layer while a sensing current is applied, however, in reality, in the presence of the applied sensing current, the magnetization in the end regions of the free magnetic layer is aligned in the track width direction and the magnetization in the central region of the free magnetic layer is distributed differently in relation to the height direction. The different directional distribution of the magnetization in the central region is caused by the magnetic field from the sensing current, the static magnetic field between the free magnetic layer and the pinned magnetic layer, and the like.
In accordance with Japanese Patent Publication No. 9-92907, by inclining the magnetization of the pinned magnetic layer (second ferromagnetic layer), the relative angle between the magnetization of the pinned magnetic layer and the magnetization of the free magnetic layer (first ferromagnetic layer) in the central region can be set at 90xc2x0 or its approximation, however, the relative angle between the magnetization of the pinned magnetic layer and the magnetization of the free magnetic layer in the end regions cannot be set at 90xc2x0, resulting in the deterioration of asymmetry.
In accordance with the present invention, as shown in FIG. 1, by inclining the magnetization G in the central region of the pinned magnetic layer 2 in relation to the Y1 direction (direction of the leakage magnetic field from the recording medium), the relative angle between the magnetization C2 of the free magnetic layer 4 and the magnetization G of the pinned magnetic layer 2 is set at 90xc2x0 or its approximation by the static magnetic field caused by static magnetic coupling, and thus, the relative angle between magnetizations C1, C2, and C3 in the entire central region of the free magnetic layer 4 and the magnetization G of the pinned magnetic layer 2 can be set at 90xc2x0 or its approximation.
Also, since magnetizations A and B in the end regions of the free magnetic layer 4 are aligned in the X direction (track width direction), magnetizations E and F in the end regions of the pinned magnetic layer 2 are aligned in the Y direction so that the relative angle between magnetizations A and B of the free magnetic layer 4 in the end regions and magnetizations E and F of the pinned magnetic layer 2 are set at 90xc2x0.
As described above, in accordance with the present invention, with respect to the pinned magnetic layer, the magnetization in end regions in relation to the track width and the magnetization in the central region are adjusted to different directions so that the relative angle between the magnetization of the free magnetic layer and the magnetization of the pinned magnetic layer is set at 90xc2x0 or its approximation in the entire region, and thus, satisfactory asymmetry can be obtained and a servo error and the like can be prevented.
In the method for making a spin-valve type thin film element of the present invention, first, magnetic annealing is performed at the temperature T1, the magnetization H of the pinned magnetic layer 2 is adjusted to the direction inclined by xcex8 in the X direction in relation to the Y direction, as shown in FIG. 2A.
After hard magnetic bias layers 5 and 5 are magnetized in the Y direction at a room temperature that is lower than the temperature T1 (refer to FIG. 2B), annealing is performed without applying a magnetic field at the temperature T2 so that magnetizations E and F of the pinned magnetic layer 2 in the end regions are set in the Y direction by ferromagnetic coupling between the hard magnetic bias layer 5 and the pinned magnetic layer 2 (refer to FIG. 2C).
As shown in FIG. 2C, since the central region of the pinned magnetic layer 2 is not strongly influenced by the coupled field between the hard magnetic bias layer 5 and the pinned magnetic layer 2, the magnetization G in the central region is put into a single domain state and fixed in the originally magnetized direction, that is, the direction inclined by xcex8 in the X direction in relation to the Y direction.
After the magnetization of the pinned magnetic layer 2 is fixed in the proper direction as described above, when the hard magnetic bias layers 5 and 5 are magnetized in the X direction, as shown in FIG. 3A, magnetizations A and B of the free magnetic layer 4 in the end regions are adjusted to the track width direction (X direction), and magnetizations C1, C2, and C3 of the free magnetic layer 4 in the central region repulse the magnetization of the pinned magnetic layer 2 owing to static magnetic coupling between the pinned magnetic layer 2 and the free magnetic layer 4, and are inclined as shown in the drawing.
When a sensing current is applied, as shown in FIG. 3B, magnetizations C1, C2, and C3 of the free magnetic layer 4 in the central region are inclined by xcex8 in relation to the X direction, and the relative angle between the magnetization of the free magnetic layer 4 and the magnetization of the pinned magnetic layer 2 is set at substantially 90xc2x0 in the entire region.